I'm hitting 2 performance issues (in .77 and .78)...
1. Sometimes songs stutter for a split second. It doesn't happen to every song and I can't really pin it down, but it might be when the computer is somewhat busy. Note I never had this problem in MC 11.
2. The CPU usage for visualizations seems to be quite a bit higher in MC 12 then it was in MC11. Actually, the CPU usage for showing MC at all seems quite high here's some data while playing a track:
MC minimized - 4% usage
MC in normal view (with mini spectrum analyzer turned off) - 6%
MC in Display View (Clean & Tidy) - 36%
MC in Display View (entirely empty visualization) - 36%
I'd say the last one is the weird one. I removed all elements from the visualization so it is just a black screen and it's still using 36% CPU.
Note: I have a dual core CPU so all of the usages above would be twice those numbers on a single core of the same speed.